PTPN22 and rheumatoid arthritis: Other genes, such as PTPN7, which are regulated by ERK1/2 and p38 [23], could be associated with chronic proliferation and avoidance of cell death through apoptosis, as has been reported for the PTPN22 gene, whose high expression has been associated directly with the inflammation and with loss of tolerance in RA [24, 25].